In a cellular communication environment, serious interference can occur in a cell boundary area when neighboring cells use the same frequency. Accordingly, the cellular communication system may provide various methods for decreasing inter-cell interference while improving a capacity of a cell boundary. In one method, in a cellular communication system, a central controller constructs a virtual cell with a plurality of neighboring cells considering an instantaneous channel value of a terminal located at a cell boundary and a traffic situation, and allows the plurality of cells constituting the virtual cell to collaborate and communicate. As illustrated in FIG. 1 for example, a scheme is provided in which, in a cellular environment in which one macro cell 100 and a plurality of pico cells 110-1 to 110-4 coexist, a central controller 120 selects the one macro cell 100 and the two pico cells 110-1 and 110-2 located adjacent to a terminal 102 for the terminal 102 located at a boundary of the pico cells 110-1 and 110-2, and forms a virtual cell with the selected one macro cell 100 and two pico cells 110-1 and 110-2, whereby the one macro cell 100 and the two pico cells 110-1 and 110-2 collaborate and communicate.
The introduction of a microwave (i.e., millimeter (mm) wave) system to secure a wide frequency band is expected. The millimeter wave system takes beamforming technology into consideration to overcome a propagation path loss caused by a high frequency band. The beamforming technology means a technology of communicating by reconciling beam directions between a Base Station (BS) and a terminal through beam training between the BS and the terminal.
The millimeter wave system may form a virtual cell with a plurality of cells and communicate in collaboration so as to reduce inter-cell interference while improving a capacity of a cell boundary. However, a method of forming a virtual cell according to the conventional art has been proposed based on a BS having an omni-directional antenna, so it may be unsuitable in forming a virtual cell with cells to which beamforming technology is applied. For instance, when forming a virtual cell with cells to which beamforming technology is applied according to the conventional scheme, the conventional method has to perform a procedure of performing beam training about all beam indexes by the BS and selecting a specific beam index that will communicate with a terminal. Thus, there is a disadvantage of being inefficient because energy waste and delay caused by beam training increase.
Accordingly, there is a need to provide a way of efficiently forming a virtual cell between cells to which a beamforming technology is applied.